Flip4Mac is the playback engine for wmv content. There are a lot of variables when thinking about why any particular video might not be playing back properly, or in the right time frame. I guess the first thing to ask, in your case, is for a link to the video you're trying to play. If you post that, then we can try it out and see if does the same thing. Aside from that, I heard that the latest version of F4M functions a little differently with regards to streaming video...and in fact, it does not stream now, but has to download first.
I might suggest you get on the F4M forum, <a href="http://forum.flip4mac.com/forum/">HERE</a>, and ask their moderator about these related issues.
And finally, here's a link to some wmv content for you to test.
http://asp.net/learn/videos/ See if any of those require excessive time to playback.